This study was designed to explore how Korean preschool and kindergarten teachers understand teacher research and utilize it in professional development. Two teachers, two site directors, and one district supervisor were interviewed in South Korea. Data were collected in multiple ways: (1) open-ended individual interviews; (2) participants' documentation (e.g., past or current teacher action research, reports, lesson plans, and journals); and (3) researcher's own experiences and memories in a teacher education program which highlighted the principle of teacher research. First, findings showed that Korean teachers, directors, and district supervisors were not familiar with the term "teacher research" due to diverse terms in Korean that refer to teacher action research; Second, Korean teachers did not consider their classroom-based experimental inquiry to be teacher research as it is not published; Third, Korean teachers conducted action research in their classrooms to develop their practice for other teachers' use, never used a self-study framework; Fourth, teacher action research competitions were centralized in the K-12 public schools; Fifth, despite that teacher action research was mandatory for public kindergarten teachers, Korean teachers encountered dilemmas teaching and doing research. Overall, this study contributes to early childhood educators and administrators in South Korea by introducing them about what is teacher research, and helping them comprehend teacher research as a form of self-initiated professional development.